Buildings for residential, commercial, and agricultural construction can have a skeletal structure typically including a floor which supports one or more walls upon which a ceiling and roof are mounted. The ceiling and roof are typically formed by a roof truss, generally formed in a triangular shape which forms, at its lower surface, a ceiling for the interior of the structure and, at its upper surface, a roof for the exterior of the structure. The roof truss may define space for an attic or the like.
One category of roof trusses are metal plate connected (“MPC”) wood trusses, in which wood truss members are coupled by metal connector plates. The wood truss members can be sawn lumber or engineered wood, such as but not limited to laminated veneer lumber, laminated strand lumber, parallel strand lumber, plywood, and oriented strand board. Sawn lumber is harvested lumber that is finished or planed, and cut to standardized width and depth dimensions.
Sawn lumber is generally categorized into the following three groups depending on size: boards, dimensional lumber, and timbers. Sizes of sawn lumber are specified using a nominal nomenclature. For example, 2×4 dimensional lumber actually measures 1½″×3½″. Other nominal sizes consist of 2×2 (actually 1½″×1½″), 2×3 (actually 1½″×2½″), 2×6 (actually 1½″×5½″), 2×8 (actually 1½″×7¼″) and others. Similar nominal nomenclature can be applied to engineered wood.
FIG. 1 shows some non-limiting conventional pieces of dimensional lumber. Different trusses use dimensional lumber in different orientations. Each orientation has its own advantages and disadvantages depending on the application. For example, a “2×” truss configuration refers to a truss in which all truss members are oriented such that their width when viewed from the front is 1½″. The depth of all truss members is also equal when viewed from the side and dependent on the dimensional lumber used; for example, using 2×4 dimensional lumber results in a depth of 3½″ while using 2×3 dimensional lumber results in a depth of 2½″. Along the same lines, a “4×” truss configuration refers to a truss in which all truss members are oriented such that their width when viewed from the front is 3½″. FIG. 1(a) illustrates this point by showing a piece of 2×4 dimensional lumber oriented in a 2× configuration, whereas FIG. 1(b) shows a piece of 2×4 dimensional lumber oriented in a 4× configuration. In the 4× configuration the lumber may be referred to as 4×2 or 2×4 (flat). FIGS. 1(c) and 1(d) show different orientations using 2×3 dimensional lumber. The “3×” truss configuration of FIG. 1(d) refers to a truss in which all truss members are oriented such that their width when viewed from the front is 2½″. In the 3× configuration the lumber may be referred to as 3×2 or 2×3 (flat).
MPC wood trusses can be produced in different shapes and sizes. While various terms can be used to describe different exterior shapes and interior web configurations, there are three basic kinds: pitched truss, vertical parallel chord truss, and horizontal parallel chord truss.
FIG. 2 is a front view of a typical prior art pitched truss 10 using a 2× truss configuration. The pitched truss 10 typically includes a bottom chord 12, which can be mounted to the walls of the building, and two top chords 14 which are mounted to the outer ends of the bottom chord 12 at a heel 16 and meet at a peak 18. A portion of the top chords 14 may extend past the heel 16 to form an eave overhang 20. The chords 12, 14 may be single lengths of wood, or may be made up of shorter sections of wood connected at a splice 22, two of which are shown in FIG. 2 for exemplary purposes. Diagonal webs 24 extend between the bottom chord 12 and the top chords 14 for structural support. Conventional metal plates 26 typically accomplish many of the fixed connections between the wood members of the truss 10, and can be nailed into the wood members.
The pitched roof truss configuration provides open space within the confines of the chords 12, 14 and webs 24, which can be used for storage and/or living space. Generally a 2×10 or 2×12 bottom chord 12 is used to handle these storage or occupancy loads. However, a single bottom chord 12 has only a limited amount of strength and stiffness, thereby requiring something with more depth. In view of this, truss manufactures have incorporated a parallel chord truss configuration into roof trusses.
FIGS. 3-4 are front views of typical prior art parallel chord trusses 30, 32, in which the bottom and top chords 34, 36 are parallel. The vertical parallel chord truss 30 has the lumber oriented vertically, i.e. in a 2× truss configuration, while the horizontal parallel chord truss 32 has the lumber oriented horizontally, i.e. in a flat, 3×, or 4× truss configuration. Of the two parallel chord trusses, the horizontal parallel chord truss 32 is generally stronger, stiffer, and more economical compared to the vertical parallel chord truss 30, all other factors being equal. When the lumber is oriented vertically, these designs generally sacrifice open space within the interior portion of the truss.
Parallel chord trusses 30, 32 are sometimes used as joists in roof trusses. Some roof trusses have incorporated a vertical parallel chord type configuration. FIG. 5 is a front view of a first example of a prior art roof truss 40 with a vertical parallel chord configuration, which uses metal plates 42 as connectors. FIG. 6 is a front view of a second example of a prior art roof truss 44 with vertical parallel chord type configuration, which uses a combination of metal plates 46 and metal web members 48 as connectors. The metal web members 48 can be, for example, V-shaped members sold by MiTek under the name Posi-Strut®.
Other roof trusses, examples of which are shown in FIGS. 7-10, incorporate a horizontal parallel chord type configuration, in which the bottom chord is provided in the form of a horizontal parallel chord truss joist. These trusses have an upper top chord with a 2× truss configuration and a lower horizontal parallel chord truss joist having a non-2× truss configuration, and accommodate for this dimensional change in different ways.
FIG. 7 is a front view of a third example of a prior art roof truss 50 with a horizontal parallel chord type configuration. The roof truss shown is a 7/12 pitch truss 50 with two upper top chords 52 having a 2× truss configuration and a lower horizontal parallel chord truss joist 54 having a 3× or 4× truss configuration fastened together with a hanger-style metal connector 56 near the heel.
FIG. 8 is a front view of a fourth example of a prior art roof truss 60 with a horizontal parallel chord type configuration. The roof truss shown is a 12/12 pitch truss 60 with two upper top chords 62 having a 2× truss configuration and a lower horizontal parallel chord truss joist 64 having a 3× or 4× truss configuration fastened together with a hanger-style metal connector 66 near the heel.
FIG. 9 is a front view of a fifth example of a prior art roof rafter system 70 with a horizontal parallel chord type configuration. The roof rafter system 70 shown is a cape style, and includes two upper rafters 72 having a 2× truss configuration and a lower horizontal parallel chord truss joist 74 having a 4× truss configuration. The upper rafters 72 are fastened to the side face of the horizontal parallel chord truss joist 74 with mechanical fasteners such as nails, screws, or lag screws, and a plywood web 76 as shown in FIG. 10, which is a detailed view of the heel of the roof rafter system 70 shown in FIG. 9.